The Milky Way Galaxy

1. The Milky Way Galaxy The Milky Way Galaxy • A galaxy is a large group of stars, gas and dust held together by gravity, • The Milky Way is a great disk made of stars orbiting a central point in the disk. • Our Milky Way galaxy is about 13 billion years old. • Our Sun is just one of perhaps 100 billion stars that make up the Milky Way.

2. The Milky Way Galaxy Discovering the Milky Way • It is difficult to see the Milky Way’s size and shape not only because are we too close, but we are also inside the galaxy. • We also cannot tell where its center is, or what Earth’s location is within it.

3. The Milky Way Galaxy The Shape of the Milky Way • Astronomers have been able to determine the galaxy’s shape by mapping it with radio waves. • Its mostly a flattened disk with a large center.

4. The Milky Way • The larger center section is called the nuclear bulge. • The halo is the region around the nuclear bulge and disk where globular clusters are located. • They make up about 90% of the galaxy.

5. The Milky Way Galaxy The Shape of the Milky Way The Milky Way consists of a nuclear bulge in the center of a disk. The disk and bulge are surrounded by a spherical region called the halo. (not to scale)

6. The Milky Way Galaxy Globular Clusters • Globular clusters are huge, spherical clusters of stars. • Globular clusters in the halo of the Milky Way, which are estimated to be as old as 12 to 14 billion years, are the oldest-known objects in the galaxy.

7. The Milky Way Galaxy Types of Galaxies • There are three types of galaxies: spiral, elliptical and irregular.

8. The Milky Way Galaxy The Shape of the Milky Way Spiral Arms • The Milky Way has four major spiral arms and numerous minor arms. • The Sun is located in the minor arm Orion at a distance of about 28,000 ly from the galactic center. • The Sun’s orbital speed is about 220 km/s, and thus its orbital period is about 240 million years.

9. The Milky Way Galaxy The Shape of the Milky Way Spiral Arms

10. The Milky Way Galaxy • Our Milky Way galaxy is a spiral one and our solar system is located on one of its arms. It is estimated that our solar system has orbited the galaxy about 20 times in its 5 billion year existence.

11. Also, most new stars form in the arms because of the amount of dust and gas located there. The center consisting of the bulge and halo are made of old stars and leftover heavy elements • The middle part of the galaxy is the oldest, where the oldest stars are found. Today we believe that there is a black hole at the center of our galaxy that we rotate around.

12. The Milky Way Galaxy Section Assessment 3. Identify whether the following statements are true or false. ______ The Sun has orbited the galaxy approximately 20 times in its history. ______ Our solar system is located at the center of the galaxy. ______ There is a black hole at the center of the Milky Way galaxy. ______ The Milky Way is an elliptical galaxy. true false true false

13. End of Section 1

14. Other Galaxies in the Universe Other Galaxies in the Universe • Our galaxy is just one of billions of galaxies in the universe. • In 1924, Edwin Hubble discovered the Andromeda galaxy. • It is our nearest neighbor. • It is speeding towards us and will one day collide into us!

15. Other Galaxies in the Universe Classification of Galaxies • There are two classifications of spiral galaxies: Barred and normal. The barred seem to have a bar through the center of them.

16. Other Galaxies in the Universe Discovering Other Galaxies Classification of Galaxies

17. Other Galaxies in the Universe Groups and Clusters of Galaxies • Most galaxies are located in groups, rather than being spread uniformly throughout the universe. • The Milky Way belongs to a small cluster of galaxies called the Local Group which is roughly 2 million ly in diameter. • There are about 35 known members including the Milky Way and Andromeda Galaxies, but most of are dwarf ellipticals. • A supercluster is an even larger cluster of galaxies.

18. Other Galaxies in the Universe The Expanding Universe • In 1929, Edwin Hubble, by measuring the redshifts and distances of many galaxies, found that the farther away from Earth a galaxy is, the faster it is moving away. • The universe is expanding, still moving outward!

19. Other Galaxies in the Universe Quasars • In the 1960s, astronomers discovered another new type of object that looked like ordinary stars, but were strong radio emitters. • A quasar is a very bright, starlike object that emits strong radio waves.

20. Other Galaxies in the Universe Section Assessment 1. Match the following terms with their definitions. ___ supercluster ___ radio galaxy ___ active galactic nucleus ___ quasar B A D C A. galaxies that emit as much or more energy in radio wavelengths than they do in visible light B.organizations of clusters of galaxies that are hundreds of millions of light years in size C.starlike objects with emission lines in their spectra D. galaxy cores that emit as much or more energy than the rest of the galaxy

21. End of Section 2

22. Cosmology Cosmology • Cosmology is the study of the universe, its current nature, and its origin and evolution. • Astronomers use a combination of observations and theoretical models in cosmology.

23. Cosmology Models of the Universe • The fact that the universe is expanding implies that it had a beginning. • The Big Bang theory is the theory that the universe began as a point and has been expanding ever since. • The steady-state theory proposes that the universe is the same as it has always been and new matter is being created as the universe expands maintaining its density. • The evidence from observational tests weighs in favor of the Big Bang.

24. Cosmology The Big Bang Model • In the Big Bang model, there is a competition between the outward momentum of the expansion of the universe and the inward force of gravity as the matter in the universe acts to slow the expansion.

25. Cosmology The Big Bang Model • Three possible outcomes for the universe include: • an open universe, in which the expansion will never stop • a closed universe, in which the expansion will stop and turn into a contraction • a flat universe, in which the expansion will slow to a halt in time—but it will never contract

26. End of Section 3

27. Chapter Resources Menu Chapter Resources Menu Study Guide Section 31.1 Section 31.2 Section 31.3 Chapter Assessment Image Bank

28. Section 31.1 Study Guide Section 31.1 Main Ideas • Because our solar system is inside the Milky Way galaxy, it was difficult at first for astronomers to determine the size and shape of our galaxy, and where Earth is located within it. • The Milky Way consists of a nuclear bulge, a disk, and a halo. Much of the mass of the galaxy is not visible. • It is hypothesized that the Milky Way began as a spherical cloud of gas that eventually collapsed into a disk. • Population I stars contain small amounts of heavy elements and are located in the arms and disk. Population II stars are located in the bulge and halo, and contain only trace amounts of heavy elements.

29. Section 31.2 Study Guide Section 31.2 Main Ideas • Galaxies are classified according to their shapes as normal spirals, barred spirals, ellipticals, irregulars, or dwarf ellipticals. • Most galaxies occur in clusters, which are further organized into superclusters. • The universe is expanding, and the Hubble constant, H, measures the rate of expansion. • Because it takes the light from very distant galaxies so long to reach Earth, when astronomers observe these galaxies, they are looking back in time. • Many galaxies have energetic objects or activities at their cores called active galactic nuclei.

30. Section 31.3 Study Guide Section 31.3 Main Ideas • The Big Bang theory proposes that the universe began as a single point and has been expanding ever since. • The steady-state theory proposes that the universe is the same as it always has been. • The universe is filled with cosmic background radiation that is left over from the early, hot stages in the Big Bang expansion of the universe. • In the Big Bang model, the universe could be open, closed, or flat.

31. Section 31.3 Study Guide Section 31.3 Main Ideas • The inflationary model can explain the walls and voids of the distribution of galaxies. It also predicts that the universe is flat, which is supported by observations. • Current observations indicate that an unknown force is accelerating the expansion of the universe.

32. Chapter Assessment Multiple Choice 1. How far is the Sun from the galactic center? a. 5 000 ly c. 28 000 ly b. 17 000 ly d. 55 000 ly The Sun is located about 28 000 ly from the galactic center on the minor arm Orion.

33. Chapter Assessment Multiple Choice 3. According to the Big Bang theory, a(n) ____ universe will expand forever. a. open c. inflationary b. closed d. flat In an closed universe, the expansion will stop and turn into a contraction. In a flat universe, the expansion will slow to a halt in an infinite amount of time—but will never contract. The inflationary universe model is a variation of the flat universe theory.

34. Image Bank Chapter 31 Images

35. Image Bank Chapter 31 Images

36. Image Bank Chapter 31 Images

37. Image Bank Chapter 31 Images

38. Help To navigate within this Interactive Chalkboard product: Click the Forwardbutton to go to the next slide. Click the Previousbutton to return to the previous slide. Click the Chapter Resourcesbutton to go to the Chapter Resources slide where you can access resources such as assessment questions that are available for the chapter. Click the Menubutton to close the chapter presentation and return to the Main Menu. If you opened the chapter presentation directly without using the Main Menu this will exit the presentation. You also may press the Escape key [Esc] to exit and return to the Main Menu. Click the Helpbutton to access this screen. Click the Earth Science Onlinebutton to access the Web page associated with the particular chapter with which you are working. Click the Speaker button to hear the vocabulary term and definition when available.

39. End of Custom ShowsThis slide is intentionally blank.